Nuclear Medicine · MU Sofia

4. Nuclear medicine diagnostics of endocrine system. Radioiodine – uptake test. Thyroid scintigraphy in benign and nodular thyroid diseases. Whole-body scintigraphy with I-131 in thyroid carcinoma. Application of SPECT/CT. Parathyroid scintigraphy with 99mTc MIBI and 99mTc tetrofosmin – dual-phase and subtraction scintigraphy.

Covers the thyroid and parathyroid glands and how nuclear medicine images them: the radioiodine uptake test with its procedure, normal ranges and causes of raised or lowered uptake, and thyroid scintigraphy with I-123 and pertechnetate, including hot, cold and diffuse patterns. It then explains whole-body I-131 scanning after thyroid cancer, then parathyroid imaging with MIBI, dual-phase and subtraction methods, and SPECT/CT, with a comparison table and a diagnostic algorithm.

Inside: 8 sections · 16 labelled pictures · 1 table · 15 flashcards · 6 min

Topic 4 of 50 in the MU Sofia syllabus for Nuclear Medicine (Medicine, Year 4). The free AceMed note covers it in 8 sections, about 819 words (6 min of reading), with 15 flashcards.

In this note

  1. ENDOCRINE ORGANS IMAGED
  2. RADIOIODINE UPTAKE TEST (RAIU)
  3. Procedure
  4. THYROID SCINTIGRAPHY
  5. Normal Scan
  6. Thyroid Nodules
  7. WHOLE-BODY SCINTIGRAPHY (WBS)
  8. PARATHYROID SCINTIGRAPHY

ENDOCRINE ORGANS IMAGED

Thyroid

Uses iodine to synthesize:

  • T3
  • T4

Therefore radioactive iodine and pertechnetate can be used.

Parathyroid

Produces- Parathyroid hormone (PTH)

Controls

  • Calcium
  • Phosphate

Abnormal glands can be localized using 99mTc-MIBI.

RADIOIODINE UPTAKE TEST (RAIU)

The Radioiodine Uptake Test (RAIU) measures how much radioactive iodine is taken up by the thyroid gland over a specific period.

It is a functional test, not an imaging test.

Principle-

Normal thyroid follicular cells actively transport iodine through the: Sodium-Iodide Symporter (NIS)

The thyroid cannot distinguish between:

  • Stable iodine
  • Radioactive iodine

Therefore it takes up both.

The amount of radioactive iodine absorbed reflects thyroid function.

Radiopharmaceutical

Usually I-123

Sometimes I-131 (less commonly today because of higher radiation dose).

Procedure

Step 1

Patient receives Oral capsule or liquid containing radioactive iodine.

Step 2

Wait

Usually

  • 2–6 hours
  • 24 hours

Step 3

A probe is placed over the thyroid.

The amount of radiation emitted is measured.

Step 4

Percentage uptake is calculated.

Normal Uptake

Normal values vary slightly between laboratories.

Typical values:

4- 6-hour uptake: approximately 6-18%

24-hour uptake: approximately 10–30%

Increased Uptake

Occurs when thyroid hormone synthesis is increased.

Examples:

  • Graves disease
  • Toxic multinodular goiter
  • Toxic adenoma

Decreased Uptake

Occurs when thyroid hormone synthesis is reduced or iodine uptake is suppressed.

Examples:

  • Thyroiditis
  • Exogenous thyroid hormone intake
  • Recent iodine contrast administration
  • Amiodarone (iodine-rich drug)

Clinical Indications

  • Hyperthyroidism
  • Differentiate causes of thyrotoxicosis
  • Evaluate toxic nodules
  • Assess thyroid function before radioiodine therapy

Contraindications

  • Pregnancy
  • Breastfeeding
  • Recent iodinated contrast
  • Recent excess iodine intake

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